The field of the present invention is video systems, and more particularly, video tape recording systems. In its most immediate sense, the invention relates to home video cassette recorders.
It has long been recognized that "pirate" copying of copyrighted video materials has caused economic problems in the entertainment industry. This is because a studio knows that only a fraction of the total number of ultimate consumers of video software will actually purchase a copy for their own use. Instead, many consumers will secure a copy of a movie and then copy it onto a blank cassette tape without payment of any kind to the studio.
Because of such "pirate" copying, the studio must price each legal copy of the software at a comparatively expensive level. This is because the studio must recoup its costs and earn its profits on a relatively small number of copies. Consequently, the actual market for legitimate video software is effectively diminished.
The diminished market also adversely affects the makers of video equipment such as video tape players and recorders. This is because the relatively high price of legitimate copies acts as a disincentive to purchasing and renting them, and in turn acts as a disincentive to purchasing video tape players and records.
Accordingly, many anti-copying schemes have been developed to prevent recordation of video software. In most instances, these schemes are similar in concept to a system known in the prior art as Macrovision. In this system, the synchronization portion of the video signal is altered in a predetermined way so as to make it possible to play properly on a television, but not be recordable by conventional consumer videocassette recorders.
However, this system is unsatisfactory for both legal and technical reasons It is entirely legal for persons to sell equipment which has a legal function, and picture stabilization is a function which may be legally performed. For example, if a person wishes to sell a "black box" which is adapted to defeat Macrovision encoding, it is only necessary that the "black box" have an entirely legal purpose, such as picture stabilization. The "black box" may then be advertised as a picture stabilizer, which coincidently has the further capability of defeating Macrovision encoding. Consequently, manufacturers, sellers and users of such devices may legitimately claim that they are making selling and using such devices for a perfectly legitimate end, namely picture stabilization, and that the defeating of Macrovision encoding is only an ancillary and unintended result.
Furthermore, it is comparatively easy to manufacture a "black box" which will defeat a Macrovision-encoded video recording. This is because any system which alters the synchronization of the video picture can be reverse-engineered with relative ease, since the task of defeating such a system reduces to the task of providing appropriate synchronization signals and linking them to the luminance and chroma signals which are already provided.
Additionally, it is important for economic reasons that any anti-copying scheme produce an acceptable video image when an encoded tape is replayed on a conventional video tape player/recorder. This is because a studio would not have a sufficiently large market for any encoded video tape which could be replayed only on new video equipment and not on the large installed base of older video players and recorder/players which exists now and which will continue to exist for many years in the future.